It is known to deposit palladium/nickel alloy coatings galvanically, i.e. by electrodeposition, upon conductive substrates for decorative or technological purposes from a bath consisting essentially of an aqueous solution of palladium and nickel amines with a palladium content of about 5 to 30 g per liter, a nickel content of about 5 to 30 g per liter, and other substances such as sulfonic acids or salts thereof, the palladium/nickel ratio in this solution being established such that the galvanically deposited coating contains 30 to 90% by weight palladium.
Coatings of this type can be used as a substitute for gold platings for decorative and some anticorrosion purposes.
A conventional bath of the aforedescribed type is disclosed in British Pat. No. 1,143,178. The sulfonic acid salts are there deemed to constitute brighteners which can be added to the bath to improve the aesthetic appearance of the coating.
The salts which are employed are certain salts of naphthalene sulfonic acid and aromatic sulfonamides such as the sodium salt of naphthalene-1,5-disulfonic acid, the sodium salt of naphthalene-1,3,6-trisulfonic acid, and saccharin (o-sulfobenzoic acid imide) and para-toluenesulfonamide.
In practice, the mechanical properties of the coatings thus produced are not fully satisfactory and, indeed, the brightness may not be sufficient for many decorative purposes.